Engine air flow responsive controls are useful in a variety of engine control applications such as, for example, control of fuel metering, ignition timing and exhaust gas recirculation. It has long been desired to measure engine air flow with readily available signals such as the combination of manifold vacuum and throttle position. However, manifold vacuum is not an adequate indication of engine air flow, particularly during engine operating conditions when it exceeds one-half the inlet air pressure and the rate of air flow past the throttle becomes sonic, due to the compressible nature of air flow. Accordingly, prior engine air flow responsive controls have required items such as engine speed sensors, air valves with position sensors, or other engine air flow sensors.